Pure water is pH neutral, measuring 7.0 on the 1 to 14 pH scale. Below 7 is acidic, and above is alkaline; the greater the discrepancy, the stronger the acid or alkaline agent. The benefits of drinking alkaline water are mostly subjective as it has undergone little clinical scientific testing. Because most of the foods and beverages we ingest are mildly to severely acidic, drinking alkaline water makes sense, though strong arguments suggest the benefits are imagined.
Pro - Hydration
Pure water passes through the digestive tract with minimal absorption, but the minerals contained in alkalised water increase absorption that hydrates cells throughout the body. Many alternative medicine practitioners believe this hydrating effect can cure or prevent many diseases.
Pro -- Contains Anti-Oxidants
The electrolysis process that ionises minerals causes alkalinity. The negatively charged molecules capture positively charged free radicals in your body that cause oxidation, which causes cells to age drastically by damaging their DNA.
Pro -- pH Balance
Most of what we eat and drink --- from orange juice and coffee to tomatoes and beef --- is acidic. Drinking alkaline water may counter the acidity of these foods, restoring a more balanced pH.
Pro -- Aids in the Treatment of Diseases
Patients suffering from a variety of conditions report perceived improvement from drinking alkaline water. Such medical problems include diabetes (reported drops in blood sugar), liver diseases, gastroduodenal ulcers, asthma, allergic disorders, high or low blood pressure and osteoporosis. Because cancer cells cannot grow in an alkaline environment, some believe alkaline water may treat or prevent cancer.
Con -- Does Not Balance pH
Alkaline water likely has no effect on body pH by eliminating excess acid. The human body expels excess acid in many ways, including through sweat, urine and exhalation (CO2 expelled during respiration is an acid).
Con -- Does Not Change the pH of the Stomach
Hydrochloric acid in the stomach has a pH of about 2, which is corrosive enough to eat through metal and certainly strong enough to counteract the negative ions in alkaline water. Everything that passes through the stomach becomes highly acidic.
Con - Does Not Change the pH of the Intestines
After acidification in the stomach, strongly alkaline enzymes in the intestines further break down food to advance digestion. The slight alkalinity of alkaline water would not affect the pH of the intestines even if it retained that alkalinity when passing through the stomach.
Con -- Variations in pH
Proponents of alkaline water suggest that it balances pH throughout the body, implying that the entire body has the same pH. The opposite is true, as pH varies widely throughout the body, not just in the digestive tract.
Con -- Needless Expense
Ionisers that convert pure water into alkaline water range in price from £65 to over £2,600, require maintenance, and have filters you need to buy and replace. If you want to raise your body's pH, you can do so far more cheaply simply by taking calcium or magnesium pills, or any acid-neutralising over-the-counter product such as Tums, Alka Seltzer or Milk of Magnesia.